[bewaretheirs]

The NTSB final report on this accident is here:

https://www.ntsb.gov/news/events/Pages/2019-PLD18MR003-BMG.a...

Unfortunately the shutdown of go.usa.gov broke a bunch of links from that page, but the NTSB recommendations are summarized starting on page 33 (PDF page 44) of https://www.ntsb.gov/investigations/AccidentReports/Reports/...

But the recommendations to the gas company included:

> Review and ensure that all records and documentation of your natural gas systems are traceable, reliable, and complete. (P-18-7) (Urgent)

> Apply management of change process to all changes to adequately identify system threats that could result in a common mode failure. (P-18-8) (Urgent)

> Develop and implement control procedures during modifications to gas mains to mitigate the risks identified during management of change operations. Gas main pressures should be continually monitored during these modifications and assets should be placed at critical locations to immediately shut down the system if abnormal operations are detected. (P-18-9) (Urgent)

Edit to add:

This page has currently working links to the specific recommendations:

https://www.ntsb.gov/investigations/Pages/pld18mr003.aspx

[lazide]

Thanks for the links - looks like I was right?

[bewaretheirs]

Well, my reading is that the corrective action was less "add redundant safeties" and more "have sufficient process controls in place to ensure you don't break the feedback loop during pipeline work".

One potential problem with a pressure relief valve as a safety is that it could turn into a flare/blowtorch if there is an ignition source nearby, which constrains where it can be located (and requires ongoing maintenance to ensure vegetation/etc., doesn't build up where it could get torched).